A “carbon ceramic brake disc” is a brake disc comprising a carbon ceramic material, wherein the carbon ceramic material comprises a ceramic matrix as well as carbon fibers embedded in the matrix.
In such carbon ceramic brake discs an oxidation of the carbon fibers and therefore wear occurs due to high operating temperatures. This wear cannot be reliably recognized by mere optical inspection. An improved recognition of wear is achieved by inductive methods of measurement. The principle used in this type of measurements is based on eddy current damping; either using two coils (EP 1 387 166) operating continuously, or one or two coils in pulsed operation (DE 10 2008 051 802). In these documents, the excellent correlation between the inductive measurement and a gravimetric determination of the wear is disclosed. A conventionally traded Profometer (www.proceq.com) is used as measuring device. Using this type of techniques, it is not necessary to disassemble the brake disc for measurement.
US 2013/0015849 describes a method for measuring the wear of a carbon ceramic brake disc, where a housing holding a plurality of coils is held against the brake disc.
All these techniques, which are based on determining a quality value dependent on the inductance of the brake disc, are designed for offline measurements where the measuring device is not permanently built into the vehicle, e.g. for measurements at a garage, where the vehicle is at rest, or for measurements of brake discs outside a vehicle. The measuring device is brought into physical contact with the brake disc and a parameter depending on the impedance of the coil(s) is measured.
It is found that this type of measuring device is poorly suited for being a permanent installation in the vehicle.